1. Field of the Invention
Certain manufacturing operations require the application of high levels of torque, usually to tighten two elements threaded together in order to prevent them from unscrewing. If both of the articles to be torqued together have angular cross-sections, such as squares or hexagons, the torquing operation can be readily accomplished with wrenches or equivalent tools. If one or both of the elements to be torqued together are cylindrical, they can be held in conventional chucks capable of applying the requisite radial force without such slippage as would unacceptably mar the surfaces of the elements at the high torque levels required by some manufacturing specifications.
Where one of the elements to be joined, however, is generally circular in cross-section and has smoothly sloping sides, it is not susceptible to being held or rotated by any conventional machine tool element, particularly at extremely high torque levels, for example, up to and in excess of 1,000 inch-pounds.
The existence of such a problem is illustrated in the manufacture of projectile shells, in which the smoothsided shell must be tightly joined by threads to its base in accordance with torque requirements high enough to prevent the two elements from becoming separated due to the spin imparted to the projectile when it is fired.
2. Description of the Prior Art
Various types of collet have previously been available for tightly gripping taper-shank machine tools, but applicants are not aware of such collets or chucks capable of reliably providing the high torque levels required for e.g. projectile manufacture, in a manufacturing operation, without gripping the article so forcefully as to mar its surface. For example, U.S. Pat. No. 2,995,832, Oct. 11, 1960 for a "Sleeve for Taper Shank Tools", discloses an essentially conical plastic sleeve for insertion between a correspondingly tapered tailstock or chuck, and a tool shank. Its function is to avoid any scoring of the mating metal surfaces, and to provide slippage between them under torsional shock. A metal insert in the tail end of the sleeve affords a surface for axially forcing it out of the tailstock, but it is neither capable of nor intended for imparting any rotational force to the chuck. The collet is not reinforced, and is plainly not capable of taking the torsional loads contemplated in accordance with the present invention.
U.S. Pat. Nos. 2,346,706 and 2,346,707, both issued Apr. 18, 1944 to the Jacobs Manufacturing Company, disclose versions of an adjustable chuck for holding tools with cylindrical shanks, and the U.S. Pat. No. 2,346,706 also indicates that the gripping edges provided by the chuck may alternatively be shaped to fit contours other than cylindrical ones. The collets of both patents involve the provision of a radial array of steel members held together by a rubber adhesive filler, and the interior surfaces of the steel members correspond to the cylindrical shank of the tool to be held in the collet. Both patents make it plain that all embodiments of the collet which they describe rely solely upon the metal elements, in contact with both the chuck and the workpiece, to hold the latter in place. For example, the specification of the U.S. Pat. No. 2,346,706 recites at column 2, lines 48-50, that "the inner, outer and front edges of the gripping members are exposed, that is, they are not covered by the resilient binder". This requirement of metal-to-metal contact is consistent with the requirement of a tool-holding collet that it precisely hold a tool shank without eccentricity or wobble.
Chucks employing resilient liners for other purposes, such as for tightening or removing bottle caps, are illustrated in U.S. Pat. Nos. 1,954,422 issued Apr. 10, 1934, and U.S. Pat. No. 2,449,161 issued Sept. 14, 1948, but they do not suggest any way of applying the requisite levels of torque to artillery shells or similarly shaped articles having extending sloping sides.